Chromous Ions Research Articles

The quantitative analysis of chromous ions by channelflow double electrode (CFDE) technique

The purpose of this study is to prove that the Channel Flow Double Electrode (CFDE) technique can be used to detect chromous ions, with a view to improving the materialbalance during a Fe-Cr repassivation sequence. The chromous ions are produced under flowingconditions by potentiostatic activation of a chromium single-crystal electrode and are thenoxidised downstream on a gold electrode. The experimental collection efficiency Nexp is the ratioof the collecting current for the oxidation of Cr2 to the steady state current of the dissolution ofchromium metal. The latter current is calculated using Faradays law, from the amount of materialdissolved after a long term activation. The value of Nexp is very close to the theoretical collectionefficiency N0 and it seems to be independent of the flow velocity in the range 40–120 cm s−1.This result is discussed and compared with the literature. Moreover as chromous ions arethermodynamically unstable in acidic media, an estimation of the limiting rate constant, k, of Cr2oxidation reaction is calculated to be less than 0.7 s−1.

Reduction of metallic surface oxides via an electrochemically-generated redox species

A new method is described for removing oxides from metallic surfaces via electroless reduction by the reducing member of a redox couple that is electrochemically regenerated in a closed loop. On tin-lead coatings, which are widely used to enhance the solderability retention of electronic components and circuit boards, naturally-formed oxides are reduced to the metallic state within ten seconds by either vanadous or chromous ions in acidic sulfate solution. Wetting balance data for wire specimens show thet this reduction treatment is an effective means of restoring and ensuring solderability.

Nucleation Mechanism and Kinetics of Hydrogen Reduction of Nickel from Aqueous Solutions with Chromous Ions as Nucleating Agent

This paper presents an experimental study on the nucleation mechanism and kinetics of hydrogen reduction of nickel from ammoniacal ammonium sulfate solutions with homogeneous nucleation by chromo us ions at 343–373 K and over the hydrogen pressure range of 0.67 × 103−2.05 × 103 kPa. Visual observations of experiments, as they proceed, in an ambient-pressure glass-reactor system are described. Nucleation of nickel embryos by chromous ions is found to be both heterogeneous and electrochemical in nature. In aqueous solutions, the homogeneous precipitation of Cr(OH)2 and Cr(OH) 3 appears to be the precursor to the electrochemical reduction of the nickel ions by chromous ions on these precipitates. The kinetics of the hydrogen reduction reaction is examined as a function of reduction reaction conditions. The reaction is very rapid and proceeds almost to completion (Ni < 100 ppm) in about 10 min. It is independent of initial nickel concentration, proportional to the square root of chromous concentration added, and 1.7 order with reference to hydrogen pressure. The apparent activation energy of the reduction reaction with hydrogen was determined to be 76 kJ mol−1 and the reduction reaction was found to be chemically controlled. Résumé Cet article présente une étude expérimentale des mécanismes de germination et de la cinétique de réduction du nickel par l’hydrogène à partir de solutions de sulfate d’ammonium ammoniacal présentant une germination homogène par ions-chrome à 343–373 K dans un intervalle de pression d’hydrogene variant de 0.67 × 103 à 2.05 x 103 kPa. Des observations visuelles de l’expérience sont présentées au cours du procédé se déroulant dans un réacteur de verre à pression ambiante. La germination des embryons de nickel à partir des ions-chrome s’avère étré de nature hétérogène et électrochimique. Dans des solutions aqueuses, la précipitation homogène de Cr(OH)2 et Cr(OH)3 est la première étape de la réduction électrochimique des ions-nickel par les ions-chrome de ces précipités. La cinétique de la réaction de réduction par l’hydrogène est étudiée en fonction des conditions de réduction. La réaction est très rapide et presque complétée (Ni < 100 ppm) après environ 10 minutes. Elle est indépendante de la concentration initiale en nickel, proportionnelle à la racine carrée de la concentration de chrome ajoutée et affectée d’un exposant 1.7 par rapport à la pression d’hydrogène. L’ énergie d’activation apparente de la réduction par l’hydrogène a été estimée à 76 kJ mol−1 et la réaction semble étré chimiquement contrôlée.

Nucleation Mechanism and Kinetics of Hydrogen Reduction of Nickel from Aqueous Solutions with Chromous Ions as Nucleating Agent

This paper presents an experimental study on the nucleation mechanism and kinetics of hydrogen reduction of nickel from ammoniacal ammonium sulfate solutions with homogeneous nucleation by chromo us ions at 343–373 K and over the hydrogen pressure range of 0.67 × 103−2.05 × 103 kPa. Visual observations of experiments, as they proceed, in an ambient-pressure glass-reactor system are described. Nucleation of nickel embryos by chromous ions is found to be both heterogeneous and electrochemical in nature. In aqueous solutions, the homogeneous precipitation of Cr(OH)2 and Cr(OH) 3 appears to be the precursor to the electrochemical reduction of the nickel ions by chromous ions on these precipitates. The kinetics of the hydrogen reduction reaction is examined as a function of reduction reaction conditions. The reaction is very rapid and proceeds almost to completion (Ni < 100 ppm) in about 10 min. It is independent of initial nickel concentration, proportional to the square root of chromous concentration added, and 1.7 order with reference to hydrogen pressure. The apparent activation energy of the reduction reaction with hydrogen was determined to be 76 kJ mol−1 and the reduction reaction was found to be chemically controlled. Résumé Cet article présente une étude expérimentale des mécanismes de germination et de la cinétique de réduction du nickel par l’hydrogène à partir de solutions de sulfate d’ammonium ammoniacal présentant une germination homogène par ions-chrome à 343–373 K dans un intervalle de pression d’hydrogene variant de 0.67 × 103 à 2.05 x 103 kPa. Des observations visuelles de l’expérience sont présentées au cours du procédé se déroulant dans un réacteur de verre à pression ambiante. La germination des embryons de nickel à partir des ions-chrome s’avère étré de nature hétérogène et électrochimique. Dans des solutions aqueuses, la précipitation homogène de Cr(OH)2 et Cr(OH)3 est la première étape de la réduction électrochimique des ions-nickel par les ions-chrome de ces précipités. La cinétique de la réaction de réduction par l’hydrogène est étudiée en fonction des conditions de réduction. La réaction est très rapide et presque complétée (Ni < 100 ppm) après environ 10 minutes. Elle est indépendante de la concentration initiale en nickel, proportionnelle à la racine carrée de la concentration de chrome ajoutée et affectée d’un exposant 1.7 par rapport à la pression d’hydrogène. L’ énergie d’activation apparente de la réduction par l’hydrogène a été estimée à 76 kJ mol−1 et la réaction semble étré chimiquement contrôlée.

Kinetics of the Ferrous/Ferric Electrode Reaction in the Absence of Chloride Catalysis

The kinetics of the ferrous/ferric redox electrode reaction has been investigated by many workers as a simple, uncomplicated charge transfer reaction which seems ideal for testing experimental techniques and charge transfer theories. However, it has only recently been understood that very small traces of chloride can have a considerable effect on the reaction rate. The relation between the chloride content of the solution and the rate constant of the ferrous/ferric reaction on a gold electrode in perchloric acid solutions is confirmed in this work. The chloride effect free apparent standard rate constant is found to be , which is two to three orders of magnitude smaller than the rate constants normally reported for this reaction if the chloride content of the solution is not scrupulously controlled. Measurements were carried out by using two different in situ methods for cleaning the working electrode surface rather than employing extensive solution purification. In the first method the measuring electrode was potentiostated at sufficiently negative potentials to desorb the chloride from the surface followed by a potential step to the equilibrium potential and a pulse measurement of the kinetics. In the second method chloride ions were removed from the surface before and during the kinetic measurement by continuous oxidation of chromous ions added in small concentration to the test solution. Good agreement was found among the rate constants determined by these methods and a reported rate constant determined in ultraclean solution.

Anodic dissolution of chromium in acidic sulphate solutions

Active anodic dissolution of chromium in acidic sulphate solutions was investigated by using the rotating ring—disc electrode ( rrde). Chromous ions dissolved from the chromium disc could be collected on the gold ring electrode by oxidation to chromic state. The empirical collection number was estimated to be 0.052, although the theoretical value was 0.24. The current of active anodic dissolution gave two Tafel regions with the Tafel slope of 0.03 and 0.12 V decade −1 in the lower and higher current density regions, respectively. The pH value of the solutions did not affect the dissolution current. The increase in sulphate anion concentration reduced the current in the higher cd region. In order to interpret the experimental results on the active dissolution of chromium, a new mechanism was proposed, which was similar to the Bockris mechanism in the case of the iron dissolution. Passivation of chromium was found to take place without relation to active dissolution. It was concluded that the passivation was attributable to the formation of the trivalent chromium oxide such as CrO(OH).

Reduction d'acetals γ-bromo α-acetyleniques par les sels chromeux : Acces aux acetals et aldehydes α-alleniques.

Abstract Reduction of γ-bromo α-acetylenic acetals 1 with chromous ions (THF + HMPA) in the presence of AcOH affords α-allenic acetals 2 whose careful hydrolysis yields the corresponding aldehydes 3 . A new access to the dried bean beetle pheromone (racemic), via a Witting reaction with 3a is reported.

Réduction par les ions chromeux de derives bromopropargyliques en composés alléniques. application à la synthese de la phéromone de la bruche du haricot sec

The racemic title compound 2(E) is obtained (77%) by reduction with chromous ions (THF+HMPT solvent, with anhydrous AcOH) of 7(E) readily prepared from 4 or propargylic diethylacetal as starting materials. In the reduction of 7(E) or 7(Z) with Cr 2+, the nature and ratios of the compounds obtained ( 2(E), 2(Z). 8(E), 9(E + Z), 10(E)) are strongly dependent on solvent (THF, or THF + HMPT) and on the protonation reagent (H 2O or AcOH). These results, and an IR analysis of the organochromium species generated from 7(E) or 7(Z) (A, B and C in equilibrium), suggest two mechanisms of protonolysis of the organochromium intermediates; mainly S E2 (THF+HMPT, anhydrous AcOH) or mainly S Ei' (THF, HsO). Some unsuccessful attempts at asymmetric induction in this reaction are reported.

ChemInform Abstract: REDUCTION OF α‐ACETYLENIC Γ‐HALOACETALS BY CHROMOUS IONS: NOVEL ACCESS TO CUMULATED TRIENIC ETHERS

Chemischer InformationsdienstVolume 12, Issue 16 Preparative Organic Chemistry ChemInform Abstract: REDUCTION OF α-ACETYLENIC Γ-HALOACETALS BY CHROMOUS IONS: NOVEL ACCESS TO CUMULATED TRIENIC ETHERS A. GORGUES, A. GORGUESSearch for more papers by this authorA. LE COQ, A. LE COQSearch for more papers by this author A. GORGUES, A. GORGUESSearch for more papers by this authorA. LE COQ, A. LE COQSearch for more papers by this author First published: April 21, 1981 https://doi.org/10.1002/chin.198116188AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume12, Issue16April 21, 1981 RelatedInformation

Denaturation of DNA in the presence of chromous (Cr 2+) ions

The effect of Cr 2+ ions on the T m (melting temperature) of DNA has been investigated under appropriate conditions for the stabilization of DNA by Mg 2+ ions. A significant lowering of T m , analogous to that observed for Cu 2+ under normal conditions, was found, for Cr 2+ at pH = 4.2 and [Mg 2+] = 5.3 mol per mole of DNA base pair. Cu 2+ also lowers T m under similar conditions. The similarity of the effects of Cr 2+ and Cu 2+ under comparable conditions may be related to similarities in their coordination properties. It is proposed that Cr 2+ and Cu 2+ ions facilitate denaturation by holding together groups on the DNA chains in such a manner that base pairing and base stacking are inhibited. Comparative results for Cr 3+ and Co 2+ are also given for these low pH/Mg 2+ ion conditions.

Réduction d'acétals α-acétyléniques γ-halogénés par les ions chromeux: nouvel accés aux éthers triéniques cumulés.

Reduction of γ- bromo α- acetylenic acetals with chromous ions affords cumulated trienic ethers in good yield.

The preparation and polymerization of ethylene-d4

A direct method for preparing deuterated ethylene by reducing acetylene-d2 with chromous ions in a dimethylformamide/deuterium oxide mixture is described. This method gives a good yield of precursor gas of relatively high purity. The gas was polymerized with a Ziegler-type catalyst to produce deuterated polyethylene with sufficient purity and melt flow properties for use in laser fusion studies. A reaction variables study showed that polymerization of deuterated ethylene yields polymers with higher molecular weights than those obtained using normal ethylene. The study also indicated that the deuterium content of the polymer decreases with increasing reaction temperature, thus dictating that the process operates near room temperature. Several mechanical and chemical properties of the deuterated polymer were determined and are reported.

The reduction of Pseudomonas cytochrome c551 oxidase by chromous ions

The reduction of cytochrome c551 oxidase from Pseudomonas aeruginosa by Cr2+ ions was followed in the stopped-flow apparatus at a number of wavelengths. The c-haem reduction proceeded in a biphasic fashion with second-order rate constants of 2.6 X 10(5)M-1-S-1 and 4.8 X 10(4)M-1-S-1 at 25 degrees C, whereas the biphasic reduction of the d1-haem appeared to be independent of reductant concentration with rate constants of approx. 1.0S-1 and 0.25S-1 respectively. The kinetically determined difference spectra (reduced minus oxidized) for the c- and d1-haems are presented.

Redox reactions of metal ions—III: Electronic rearrangements in the precursor bridged complex of the chromium(III)-chromium(II) exchange reactions

A correlation is found between the energy of the first d− d bands of a number of Cr(III) complexes and the rate of the electron exchange reactions of the complex with chromous ions. The correlation reflects the ease of electronic rearrangement at the Cr(III)-site in the activated sate for the electron transfer reaction. The greater tetragonal distortion at the Cr(III) site, caused by some ligands attached to Cr(III), is connected with a lower reorganization energy of the precursor complex and this tetragonal distortion was evaluated from an analysis of the electronic spectrum of the Cr(III) complex taking part in the reaction. Thus electronic spectra of one of the reactants may be used to predict reaction rates of electron exchange between Cr(III) and Cr(II).

The reduction of carboxymethyl-cytochrome c by chromous ions.

The reduction of ferricytochrome c and ferricytochrome c carboxymethylated at the haem-linked methionine (residue 80) by Cr(2+) ions was studied by stopped-flow techniques. At pH6.2 the kinetics of reduction of ferricytochrome c are simple and correspond to a second-order rate constant of 1.21x10(3)m(-1).s(-1). Under identical conditions the kinetics of reduction of the carboxymethyl derivative, carboxymethyl-cytochrome c, are complex; two Cr(2+)-concentration-dependent processes (1.5x10(4)m(-1).s(-1) and 1.3x10(3)m(-1).s(-1)) lead to the formation of an intermediate which decays in monomolecular fashion (0.15s(-1)) to form the normal fully reduced material. The kinetic difference spectrum for the overall process corresponds to that found statically, whereas the kinetic difference spectrum of the intermediate minus the oxidized form resembles that of the low-spin ferrous form of carboxymethyl-cytochrome c minus oxidized carboxymethyl-cytochrome c. A model is proposed in which the reduction of low-spin ferric carboxymethyl-cytochrome c to high-spin ferrous carboxymethyl-cytochrome c involves a low-spin ferrous intermediate. The monomolecular step involving the decay of this low-spin ferrous intermediate is associated with an activation energy of approx. 126kJ.mol(-1) and is thought to involve both a change of spin state and a protein-conformational event. Although carboxymethyl-cytochrome c represents a mixture of species separable on a charge basis, the above observations were independent of which species was chosen for study.

Electron transfer reactions in biological systems: the reduction of ferricytochrome c by chromous ions.

Chromous ion reacts with ferricytochrome c to yield a one-to-one Cr(III)-ferrocytochrome c complex. This material, when hydrolyzed by trypsin and subjected to chromatographic procedures, yielded two fragments containing chromium. The amino-acid compositions and chemical characteristics of each of these fragments indicated that the chromium had crosslinked two segments of polypeptide chain; these were residues 40-53-Cr(III)-residues 61-72 and residues 40-53-Cr(III)-residues 61-73. Examination of a model of the ferricytochrome c molecule indicated that only two residues of the crosslinked peptides were sufficiently close to allow crosslinking to take place. These residues were tyrosine 67 and asparagine 52. Enzymatic hydrolysis of one of those fragments by aminopeptidase M supported this identification. The position of the chromic ion implies what is the path of electron transfer from the chromous ion to the ferric ion in this chemical reduction of cytochrome c, and suggests a possible path of electron transfer in biological oxidation-reduction reactions.

Electron transport to clostridial rubredoxin: kinetics of the reduction by hexaammineruthenium(II), vanadous and chromous ions.

The rate constants (25 degrees , M(-1) sec(-1)), activation enthalpies (kcal/mol), and activation entropies (e.u.) for the second-order reduction of oxidized clostridial rubredoxin by Ru(NH(3))(6) (2+), V(H(2)O)(6) (2+), and Cr(H(2)O)(6) (2+) at I = 0.10 have been determined or estimated to be 9.5 x 10(4), approximately 1.4, approximately -31 (pH 6.3-7.0); 1.6 x 10(4), 0.1, -40 (pH 3.5-4.5); and 1.2 x 10(3), approximately 0, approximately -44 (pH 3.5-4.0), respectively. Ionic strength dependencies for the vanadium reaction are suggestive of a direct interaction of the reductants with the Fe(SR)(4) (-1) site of oxidized rubredoxin. The results are consistent with outer-sphere mechanisms for all three reductants and an especially high inherent outer-sphere reactivity of rubredoxin. This high reactivity level is attributed to the low activation enthalpy demands of the iron-sulfur site of rubredoxin. Thus, the possibility is raised that the rate of reaction of rubredoxin with its physiological counterparts may be determined largely by the activation entropy demands imposed by the physiological reactant. Evidence is presented in support of an absolute entropy decrease of about 7.5 e.u. on going from oxidized to reduced rubredoxin, which is presumably attributable to the charge increase from Fe(SR)(4) (1-) to Fe(SR)(4) (2-) at the redox site.

An investigation of phonon scattering by chromous ions in MgO by thermal conductivity measurements

The effects of X -irradiation, thermoluminescence and heat treatment on the thermal conductivity principally between 1 and 4 °K of nominally pure and Cr-doped MgO have been examined. It is concluded that the Cr2+ion produced by X -irradiation is responsible for the very strong excess phonon scattering. An analysis of the data shows that the scattering has both resonant and non-resonant components and that if the non-resonant component is proportional to concentration, the resonant component is proportional to the square root of the concentration indicating the existence of cooperative effects. The resonant scattering occurs atca. 4 cm-1in reasonable agreement with the calculated energy separation 5.6 cm-1of theEandA2levels of Cr2+(Fletcher &amp; Stevens 1968). The work also indicates that the thermal conductivity at 4.2 °K provides a useful method of determining the Cr2+concentration in MgO.

The acoustic paramagnetic resonance of chromous ions in magnesium oxide

Observation of acoustic paramagnetic resonance of chromous ions in magnesium oxide at 9.46 GHz and 16 GHz confirms that the energy levels have either four-fold or two-fold symmetry in the [001] plane while the energy levels which give transitions at both frequencies appear to be linear with magnetic field.

The acoustic paramagnetic resonance spectrum of chromous ions in magnesium oxide

The acoustic paramagnetic resonance spectrum of the chromous ion as an impurity in magnesium oxide has tetragonal symmetry. There are three sets of chromous ions each giving a spectrum with its fourfold axis of symmetry along a direction in the magnesium oxide. The three sets of ions can be aligned by the application of external uniaxial compression. The results are consistent with the chromous ion undergoing a dynamic Jahn-Teller effect and there being a distortion from cubic symmetry at each chromous ion site due to random internal strains in the crystal.